The Excited State Properties of Thermally Activated Delayed Fluorescence Emitters: A Computational Study Towards Molecular Design

热激活延迟荧光发射体的激发态特性：分子设计的计算研究

• 批准号: EP/N028511/1
• 负责人: Thomas Penfold
• 金额: $ 10.97万
• 依托单位: Newcastle University
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2016
• 资助国家: 英国
• 起止时间: 2016 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=EP%2FN028511%2F1
• 关键词: Excited; State; Properties; Thermally; Activated

Lighting and displays form essential parts of our daily lives and consume approximately 20% of the electricity used worldwide. Consequently, significant energy and cost savings can be achieved by improving the efficiency of these devices. Due to their lightweight, flexibility and high-performance optical and electrical properties, Organic Light-Emitting Diodes (OLEDs) are a central focus of this research and have huge potential for application in technologies such as smart phones, televisions and lighting. OLEDs are, like classic LEDs, able to transform electrical energy into visible, ultra-violet (UV) or near Infra-red (NIR) light. However, unlike LEDs, OLEDs consist of several very thin, stacked layers organic materials and do not rely on small, point-shaped single crystals. In addition, organic systems are highly attractive for mass production stemming from their ability to be deposited on a variety of low-cost substrates such as glass, plastic or metal foils, and due to their relative ease of processing. Indeed, because production costs of these devices are typically dominated by fabrication and packaging, the relatively weak van der Waals bonded organic films also create the opportunity for a new suite of innovative fabrication methods, including direct printing through the use of contact with stamps, or alternatively via ink-jets and other solution-based methods. Even though OLEDs have huge potential to achieve a higher energy efficiency than LEDs and may also be processed under more sustainable conditions, today's state of the art white OLEDs still have higher power consumption than white LEDs. In terms of efficiency, initial attempts to implement OLEDs based upon purely organic materials were restricted by the type of excited state which emits the light. Indeed, upon electrical excitation 25% of the emitting molecules are in a so called singlet excited state, while 75% are in triplet excited states. However, conventional organic materials cannot emit from the triplet excited states, meaning that only a maximum efficiency of 25% could be achieved. An extensive research effort successfully led to 2nd generation (so called phosphorescence) OLEDs that use heavy metals to promote light emission from the triplet states and, in principal, achieve 100% efficiency. However, until now the only phosphorescent materials found practically useful are iridium and platinum complexes that are unappealing for commercial applications due to their high cost and low abundance.This research proposal seeks to investigate, using multi-scale modelling, the fundamental properties crucial to molecules and materials for a new class of OLEDs that exploits thermally activated delayed fluorescence. This exploits a small energy gap between the two emitting states (singlet and triplet) so that thermal energy can transfer population from the triplet state to the singlet state. Importantly this mechanism opens the possibility to achieve, in principal, 100% efficiency and crucially precipitates the potential to return to materials containing only lighter more abundant elements, such as organic molecules. By combing quantum chemistry, molecular and quantum dynamics, this multidisciplinary approach will produce a detailed physical and chemical understanding of the material properties on a wide variety of time and length scales. Critically, these simulations will underpin our understanding of the properties that lead to their efficiency. This bottom up approach will consequently provide important insight into achieving systematic material design with the potential for vastly improved and cheaper devices.

照明和显示构成了我们日常生活的重要部分，并消耗了全球使用的大约20％的电力。因此，可以通过提高这些设备的效率来实现大量的能源和成本。由于它们的轻巧，灵活性和高性能的光学和电气性能，有机发光二极管（OLEDS）是这项研究的主要重点，并且具有巨大的潜力，可以在智能手机，电视和照明等技术中应用。 OLED像经典的LED一样，能够将电能转化为可见的超紫色（UV）或近红外（NIR）光线。但是，与LED不同，OLED由几种非常薄的有机材料组成，并且不依赖小点形的单晶。此外，有机系统对大规模生产具有很高的吸引力，其能力源于它们在玻璃，塑料或金属箔等各种低成本底物上的能力，并且由于它们相对易于加工。确实，由于这些设备的生产成本通常由制造和包装主导，因此相对较弱的范德华（Van der Waals）粘合的有机膜也为新的创新制造方法套件创造了机会，包括通过使用邮票使用邮票的直接打印，或者通过墨水喷射和其他基于解决方案的方法进行直接打印。即使OLED具有比LED更高的能源效率的巨大潜力，并且在更可持续的条件下也可以处理，但当今最先进的白色OLED仍然比白色LED具有更高的功耗。在效率方面，基于纯有机材料实施OLED的初步尝试受到发光的激发状态的类型的限制。实际上，在电激发时，25％的发射分子处于所谓的单线激发态，而有75％的人位于三胞胎激发态中。但是，传统的有机材料不能从三胞胎激发态中发出，这意味着只能达到25％的最大效率。一项广泛的研究工作成功地导致了使用重金属促进三胞胎状态的光发射的第二代（所谓的磷光）OLED，并且主要实现了100％的效率。然而，直到现在，发现实际上有用的唯一磷光材料是由于其高成本和低丰度而对商业应用没有吸引力的磷光材料。这项研究提案旨在调查，使用多尺度建模，对新型OLEDS的分子和材料至关重要的多尺度建模，用于利用热量延迟的OLEDS的分子和材料。这利用了两个发射状态（单线和三重态）之间的较小能量差距，因此热能可以将人口从三重态转移到单线状态。重要的是，这种机制在原理上开放了100％效率的可能性，并至关重要的是恢复仅包含更丰富元素（例如有机分子）的材料的潜力。通过梳理量子化学，分子和量子动力学，这种多学科方法将在各种时间和长度尺度上产生对材料特性的详细物理和化学理解。至关重要的是，这些模拟将支持我们对导致其效率的特性的理解。因此，这种自下而上的方法将为实现系统的材料设计提供重要的见解，并具有大量改进和便宜的设备。

项目成果

World Scientific Reference on Spin in Organics - Volume 3: Magnetic Field Effects

有机物自旋世界科学参考书 - 第 3 卷：磁场效应

• DOI: 10.1142/9789813230194_0006
• 发表时间: 2018
• 作者: Dias F

Photophysics of thermally activated delayed fluorescence molecules

• DOI: 10.1088/2050-6120/aa537e
• 发表时间: 2017-03-01
• 期刊: METHODS AND APPLICATIONS IN FLUORESCENCE
• 影响因子: 3.2
• 作者: Dias, Fernando B.;Penfold, Thomas J.;Monkman, Andrew P.
• 通讯作者: Monkman, Andrew P.

Rapid predictions of the colour purity of luminescent organic molecules

• DOI: 10.1039/d1tc04748e
• 发表时间: 2022-01-07
• 期刊: JOURNAL OF MATERIALS CHEMISTRY C
• 影响因子: 6.4
• 作者: Ahmad, Shawana A.;Eng, Julien;Penfold, Thomas J.
• 通讯作者: Penfold, Thomas J.